One requirement for a wheelchair to be user-friendly is that the wheels need to be easy to remove, making it considerably easier for the wheelchair user to travel by other kinds of vehicles, such as cars, buses and trains, since the wheels can be taken off so that the wheelchair occupies less space and can be carried with the user.
For these reasons, a quick lock function has been developed for wheels on manually powered wheelchairs. Such a quick lock function is known from U.S. Pat. No. 5,482,305, in which the wheelchair has a planetary gear in the wheel hub and is provided with mechanisms for choice of gear ratio between gripping ring and wheels to make it easier for the wheelchair to negotiate gradients. The quick lock function comprises a rod which runs within the wheelshaft and which when moved in an axial direction inwards towards the wheelchair acts upon a lock so that the wheel and hub are disconnected from the wheelshaft.
As previously mentioned, planetary gears are used in wheels of wheelchairs in the same way as their very common use in cycle wheels. Change of gear position on a cycle with a planetary gear in the hub of its powered wheel is usually performed by means of a chain disposed relative to the hub shaft. The chain runs via one end of the shaft about which the wheel is supported and in through a hole along this shaft's centerline, so that the chain can act upon a gear selector for the planetary gear within the hub. To make it possible to operate the chain, it is typically fastened to one end of a wire which has its other end fitted to a gear selection positioner. The positioner is normally situated within convenient reach for the cycle rider, such as near the fingers or hands, e.g. on the handlebar, so that the rider does not even need to change the position of a hand in order to change gear. There are similar devices for setting the gear position of a wheelchair wheel planetary gear whereby a wire or equivalent pulls a chain which acts upon the gear selector in the planetary gear.
A disadvantage which arises in arranging gearchange devices for a wheelchair wheel for operating the planetary gear via a wire or other mechanism connected to the outer end of the wheelshaft is that the previously mentioned quick lock function imposes stringent requirements upon the designer if the wheel is to maintain its function of being easy and quick to remove from the wheelchair. Any wires, chains or similar devices which remain dangling from the wheel hub when the wheel is detached from the wheelshaft are in principle unacceptable.
The previously mentioned specification U.S. Pat. No. 5,482,305 refers to a mechanism which does not use a chain at the wheelshaft for setting the gear position of the planetary gear. Instead, it uses a finger disc which is disposed on the hub outside the gripping ring and is in contact with the planetary gear via a sleeve disposed around the previously mentioned rod for operating the quick wheel lock. A disadvantage of this finger disc is that changing gear entails its being rotated rearwards or forwards and being situated close to the wheel hub on the outer side of the wheel. To change gear, the user has to let go of the gripping ring and find the finger disc. This is inappropriate, for example, when the wheelchair is on a sloping running surface. Another difficulty of this known technology is that it is very difficult to incorporate more than two alternative gear positions. The user is obliged to impart his/her desired gear ratio to each wheel separately, since there is no synchronization between the gear ratios of the respective wheels.
U.S. Pat. No. 7,832,753 to the present applicant, and which is hereby included by reference in its entirety, relates to a gear shift pertaining to a hub of a wheel with a quick lock. The hub has a gear which is supported round a shaft with an outer end and an inner end. The inner end of the shaft is suspended via a suspension device on a vehicle. The quick lock includes a rod which runs in a cylindrical hole which is concentric within and with the shaft and a catch which locks the wheel with the shaft to the suspension device. The gear shift includes the shaft, the rod and a control, all of which are so adapted that the rod has a neutral position relative to the shaft and wherein a movement, relative to the shaft, of the rod from the neutral position in a direction from the outer end of the shaft towards the inner end of the shaft disengages the catch so that the wheel together with the shaft can be locked to and released from the suspension device. The rod is further provided with a gear selector contact configured to contact a gear selector in the gear, and, by a movement, relative to the shaft, of the rod in an axial direction from the neutral position in a direction from the inner end of the shaft to the outer end of the shaft, acts via the gear selector contact to cause the gear selector in the gear to change gear position so that the gear ratio of the wheel relative to a drive device for the wheel is changed.
In U.S. Pat. No. 7,832,753 the choice of gear position is controlled by a gear positioner, which in the case of wheelchair is situated within easy reach on the wheelchair frame. The gear positioner transmits the gear positions set by the user via a control which may take the form of a wire (or other elongate flexible means) or a link system to the rod which controls the gear selector in the planetary gear. A wheelchair is usually provided with two wheels driven by gripping rings. Both wheels are, according to U.S. Pat. No. 7,832,753, said to preferably be equipped with the gearchange mechanism, in which case it is stated as advantageous that the gear positioner should act on planetary gears in both wheels in order to set the same gear position for both wheels.
The gear shift according to U.S. Pat. No. 7,832,753 thus comprises a control for operating the rod in order to impart a selected gear position. According to one embodiment, the control takes the form of a wire connected to an undepicted gear positioner disposed at a location convenient to the user. According to this embodiment, a lever is disposed at the end of the control which acts upon the rod. The lever is provided with an eccentric. In a normal position arranged for the gear, the eccentric on the lever does not abut against the rod. The spring force of a return spring holds the gear stationary in the first gearchange position, here called the normal position. In response to switching of the gear positioner for selection of a second gear position, with consequent pulling of the wire, the lever pivots, with the result that the eccentric pushes the rod in and thereby causes the rod, the shaft spigot and the gear selector to set a second gear position in the gear.
Where a gear shift according to U.S. Pat. No. 7,832,753 is used on a wheelchair, it is advantageous that both of the wheelchair's wheels be subjected to approximately simultaneous gearchanging and that the same gear ratio be set for both wheels. Achieving this entails providing a gear shift according to U.S. Pat. No. 7,832,753 on each of the wheelchair's wheels, with a single gear positioner according to the examples being preferably provided to effect the gearchanging of both wheels. This is according to U.S. Pat. No. 7,832,753 for example achieved by a wire used in the control for each gear shift being operated by the same gear positioner.
However, although it has been found that such a wire operated gear change system works quite well a few drawbacks have been identified. Firstly, the described lever/eccentric mechanism requires a considerable amount of space in an axial direction within the frame of the wheelchair which limits the collapsibility of such a frame as one such mechanism is required at each wheel side. Secondly, although the requirement that the wheelchair's wheels needs to be subjected to approximately simultaneous gearchanging is usually met quite well immediately after initial application of a wire system, such systems are notoriously known to be prone to unbalance after a period of time, e.g. if the connection of a first wire arranged to pull a second wire interconnecting two systems has moved from a centrally balanced attachment position to an off-center position, gearchanging would likely take place with a short time interval between the right hand and the left hand side wheels. Such non-simultaneous gearchanging will cause discomfort to the wheelchair operator and potentially incur unnecessary strain on the mechanics of the wheelchair. Thirdly, wire operated gear change systems of this kind are sensitive to environmental influences, such as from dirt, gravel, snow, ice and slush, which may cause such systems to malfunction.
Thus, there is a need for a compact and synchronously operable gear change system useable in conjunction with wheelchair wheels of the kind described in U.S. Pat. No. 7,832,753.